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  1. Practice
  2. Data Structures
  3. Trees
  4. Tree: Postorder Traversal
  5. Discussions

Tree: Postorder Traversal

  • khushboo4tiwari + 7 comments

    void Postorder(Node root) {

    if(root == null)
    {
    return;
}
if(root!=null)
    {
     Postorder(root.left);
     Postorder(root.right);
     System.out.print(root.data+" ");

}

    }

    • dipankar4 + 0 comments

      Thanks its working and compact

    • chianghomer + 1 comment

      I think the condition check for root == null is not necessary since it's a void method.

      • whiteflags99 + 1 comment

        If you didn't have the check I think you would end up with a null pointer exception. Something has to stop the recursion.

        • chianghomer + 1 comment

          no since it is void and that we do not need the base case to stop the recursive call. If the root (or current Node) is null it just finish the call and do nothing.

          • whiteflags99 + 1 comment

            I'm getting confused about what people exactly mean. It would either be 

            if (root != null)
{
   Postorder(root.left);
   Postorder(root.right);
   System.out.print(root.data+" ");
}

            or

            if (root == null)
   return;
Postorder(root.left);
Postorder(root.right);
System.out.print(root.data+" ");

            I agree that you don't need both of the options, but one is necessary.

            • nik0mon + 0 comments

              This is the correct answer.

    • Tolani + 0 comments

      To be honest you don't need the second if statement if(root!= null) . The base case is can be seen as a else construct. I don't program in java but in C++ it looks like this

      void postOrder(node *root) {

    if(root == NULL) return;
    
    postOrder(root->left);
    postOrder(root->right);
    cout << root->data  << " ";
}

      I guess in java, it would be 

      void Postorder(Node root) {
if(root == null)
    {
    return;
    }
     Postorder(root.left);
     Postorder(root.right);
     System.out.print(root.data+" ");
}
    • RodneyShag + 0 comments

      Same idea, with less lines of code, here in my HackerRank solutions.

    • nik0mon + 0 comments

      More succint and more compact to just use 1 of the if case. To me its more readable to use the second if statement only.

    • fimka + 0 comments

      root!=null is not necessary because it is preceded by "if(root == null)", isn't it?

    • palashrawat7 + 0 comments

      Could you please explain the part :-

      Please explain the traversing.

      Postorder(root.left); Postorder(root.right);